Balky injector
 

Recently, my 92 300SE has developed a significant miss at first start-up.

Assuming an intact and properly working valve-train, it's down to spark or fuel. At the last plug change, all 6 looked by-the-book, and the car's not using any oil or burning any. Ignition system, except for the coil, is brand new.

Rev it up a bit and the problem goes away.

I'm doing some major work on the car, and as such am not driving it every day. Started it a few days ago and had the chance to check the injectors.

Missing is like 1 cylinder is dead.

Starting at the front of the motor, unplugged the 2nd injector (1st was too hard to get at), and got a noticeable downgrade in idle. Plugged it back in, back to missing on a single cylinder. Unplugged 3rd - same as second. Unplugged 4th - same as 3rd. Unplugged 5th - no change. BINGO! Plugged it back in - idle smooths out just fine.

Checked with MB and at my cost, a new injector is $130!!!

I'm thinking about trying some sort of fuel-rail added cleaner.

Is this a good idea, and are there any suggested brands?

bump...

Have you checked the dist cap & spark plug wire?

Injector failure is RARE on that most new cars!

Dist cap and plug wires are brand new.

I would have thought that when you unplug the injector and see no change, that the problem is isolated to fuel. Thinking about it further I see that if no spark is present, removing the fuel will have no effect.

I can repeat the test by pulling the plug wire and seeing if I get the same effect - although the reverse is now true - removing spark when no fuel is present will have no effect.

Wiring harness has been replaced.

I'll pull the plug and see what I find. Maybe there's a piece of crap on it that is causing misfire until everything gets a little warm.

Regardless - it couldn't hurt to run some injector cleaner through, right? I'm thinking fuel-rail administered systems - not through the tank stuff like Techron.

Any suggestions?

don't you have a coil on #5 plug and could it be the infamous coil to plug connector?

no coil on plug on a 92 300se - LH-SFI here.